Various communications protocols are known in the art. For example, the Third Generation Partnership Project (3GPP) has been working towards developing a number of protocols for use with a wireless communication path. The original scope of 3GPP was to produce globally applicable technical specifications and technical reports for a 3rd generation mobile system based on evolved Global System for Mobile communication (GSM) core networks and the radio access technologies that they support, such as Evolved Universal Terrestrial Radio Access (EUTRA) including both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes. 3GPP's scope was subsequently amended to include the maintenance and development of GSM technical specifications and technical reports including evolved radio access technologies (e.g. General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE)).
Presently, EUTRA calls for a random access channel (RACH) protocol and in particular a physical random access procedure requiring reserved resources for RACH access. The RACH channel is used for initial access to the network as well as to transmit small to medium amount of control information and data packets. This 3GPP UMTS specification permits an overall procedure that allows for various protocol/operational states to suit varying degrees of needed, anticipated, and/or desired operational activity for transmission of data packets. Unfortunately, for some desired applications using small of medium amounts of control information and data packets, the amount of data transmission activity appears to underutilize these reserved RACH resources, thereby wasting transmission resources.
The RACH (random access channel) is essential for initial access to the network, for the transmission of control information and data packets. The initial access channel has different names in different systems, such as RACH in the context of 3GPP, or ranging in the context of IEEE std. 802.16e. In this invention, we use RACH in its general sense to represent the initial access channel of communication systems.
It is desired that the RACH include a contention channel, fast acquisition of preamble, minimization of interference, minimum impact on other scheduled data transmission, and low data rate transmission for short data/control messages. Several options are available for multiplexing between the RACH and scheduled-based channels; Time Division Multiplexing (TDM), Frequency Division Multiplexing (FDM), and Code Division Multiplexing (CDM). However, in the 3GPP system problems arise for multiplexing between RACH and scheduled-based channels using either TDM or FDM. In particular, TDM requires reservation of slots for RACH access, and FDM requires a frequency (subcarrier) reservation for RACH access. In either case, a resource reservation is allotted even if there are few RACH requests in the system, which withholds unused resources that adversely affect system capacity. CDM transmission, on the other hand, will generate interference to other uplink users.
To control interference generated by CDM transmission, a MC-CDMA (multi-carrier code division multiple access) technique can be applied for RACH design without reserving system resources. This invention uses this technique for non-reserved RACH access of EUTRA communication system.
Skilled artisans will appreciate that common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.